Processing magnesium



patente& Dec. 19, 1933 UNITED STATES PATENT OFFICE Hoy, mdland, Mish.,

assignors to The Dow Chemical Company, Midland, Mich., a corpo- 'ation of Michigan Application January 5, 1933. Serial No. 650398 19 Claims.

The invention relates to improvements in processing magnesium, i. e. melting, purifying, alloying and pouring the metal. As used in the specification and claims the term magnesium" means pure magnesium or alloys thereoi wherein the magnesium content predominates.

It is well recognized that difliculties are encountered in processing molten magnesium because of the exceeding readiness with which the metal tends to oxidize, particularly at temperatures near or above its melting point. The term "oxidation" is used in its broad Chemical sense and includes the action of nitrogen, carbon dioxide, etc. upon magnesium.

To overcome the difliculties encountered due to oxidation, numerous remedies have been proposed. For instance, it has been proposed to protect the metal from oxidation by maintaining thereover a layer of a vapor non reactive therewith, e. g. sulphur vapor, thereby excluding air from contact with the metal. While the practice of this method gives satisfactory results when the entire quantity of metal is to be poured from the melting crucible at one time, it does not avoid the -loss of a substantial amount of magnesium where varying amounts of metal less than the entire content are poured intermittently from the crucible. It has been found that as the crucible is tilted a film of metal sticks to the wall thereoi which is then out of contact with the main body of metal and that this thin film oxidizes even in the presence of a protective atmosphere successive intermittent pourings result in the building up of a substantial layer of oxidation products on the steel crucible wall which, of course, means a loss of considerablemetal.

Another proposal has been to cover the surface of the molten metal with a fluid ux thereby excluding the air from contact with the metal and thus preventing oxidation. While this method is satisfactory from the standpoint of melting and purification, it interferes with the pouring of the molten metal from the melting crucible since some ux may become entrained in the metal being poured and thereby produce flaws due to ux inclusions in the finished castings.

To avoid the diiculty of fiux inclusions it has been proposed to use a flm: of a composition such that it forms a hard crust over the surface of the metal, in which crust a hole may be broken and the metal poured therethrough without the danger of flux becoming entrained the'ein. Here again is a method which can be used only when the entire crucible is to be emptied at one time, since the flux does not follow the metal level down in the crucible. Thus, if the pot is tilted back only partially emptied there will be an air space between the top of the metal and the hard flux crust and the effectiveness of the flux to protect the metal is lost.

In contrast to the foregoing, we have found that by utilizing in combination a tilting melting crucible, preferably substantially covered, for melting a body of magnesium and maintaining it molten, a fluid flux which is interposed between the molten magnesium and the crucible but does not cover the surface of the molten metal, and a protective atmosphere over the sur face of the metal to prevent oxidation thereof; we are enabled thereby to maintain a supply of molten magnesium always at hand, from which castings requiring less metal than the total content of the crucible can be pour-ed with the loss of only a negligible amount of metal due to oxidation and without the danger of inclusions of fiux in the finished castings. Furthermore, the molten magnesium can be cooled down at any time during operation of the crucible and then re-melted without contamination of the metal occurring, which eliminates the usual necessary procedure of completely emptying and cleanina out the melting crucible after each heat. Thus, in accordance with the present invention all such difiiculties as inhere to prior processes for melting, purifying, alloying, and pouring magnesium are obviated.

The invention, then, consists of the steps and means hereinafter fully described and particularly pointed out in the claims, the annexeol drawing and the following description setting forth in detail certain means and modes of Carrying out the invention, such disclosed means and modes illustrating, however, hut several of the various ways in which the principle of the invention may be used.

In said annexed drawing:

The single figure is a sectional elevation of a covered tilting melting crucible with a charge theren, and mechanism for producing a protective atmosphere over the magnesium in the crucible.

The flux which we have found suitable ti) em ploy is compounded in such manner that it possesses the following physical properties:--(l) It is fluid at temperatures slightly below the melting pointof commercial magnesium alloys, i. e. approximately 1100-1200 E; (2) it has a greater specific gravity when fluid than molten magnesium; and, (3) its surface tension is such that it is capable of forming a thin film of flux bei tween the sides of the crucible and the molten metal without tending to spread upon the surface of the magnesium.

We have found that a fiux having such properties can be prepared by admixing in suitable proportions magnesium chloride, potassium chloride, barium chloride and an alkali metal or alkaline earth metal fluoride. The potassium chloride in the foregoing composition can be replaced with the chloride of sodium or lithium. Another particularly adaptable flux can be prepared by admixing calcium chloride, sodium chloride, barium chloride, and an alkali metal or an alkaline earth metal fluoride, e. g. calcium fiuoride. The properties of specific gravity and surface tension can be varied readily by changing the proportions of the ingredients in the foregoing compositions, particularly the amount of fluoride or of barium chloride. The barium chloride particularly influences the specific gravity, while addition of a relatively small amount of a luoride increases the surface tension of the fiux.

The fluid fiux coalesces below the molten metal in the crucible and a very thin film extends up the walls of the crucible thus wetting them surficiently to prevent metal from adhering thereto. In order to absorb into the fiux the impurities present in the metal the body of fiux is occasionally intermingled therewith by puddling, particularly after introducng impure metal into the crucible. It is, then, possible to use a fiux which has a high gravity and a low surface tension; a fiux having a low gravity and a high surface tension; or a flux which has the two properties balanced. This will be understood because it is readily to be seen that a heavy fiux will require a low surface tension to enable a film thereof to creep up the crucible walls, while a light flux requires a high surface tension to keep it from spreading upon the surface of the molten metal. In the preparation of the flux the salts may be dehydrated before being mixed, which is the preferable procedure, but the hydrated forms can be mixed and melted down to obtain a substantially anhydrous flux. g

To illustrate the manner. in which the percentage of the ingredients can be varied, the composition of a suitable flux, calculated on an anhydrous basis, which we may use in practicing our invention may vary from about 80 to 30 parts by weight of calcium chloride, 20 to '70 parts of sodium chloride, 1 to 20 parts of calcium fluoride and 2 to 20 parts of barium chloride. For greatest fluidity of the molten fiux a narrower range of variation is preferable, i. e. between about 75 and 60 parts of calcium chloride, 25 and 40 parts of sodium chloride, 5 and 10 parts of caloium fluoride and about 5 to 10 parts of barium chloride.

As a specific example of the preparation of a suitable fiux approximately parts of anhydrous calcium chloride and 25 parts of sodium chloride may be melted together and 5 parts of calcium fiuoride added thereto. If it is desired to increase the density of the fiux, for instance when the flux is to be used 'n melting an alloy having a materially higher specific gravity than that of pure magnesium, about 5 parts of barium chloride may be added.

In preparing a magnesium chloride base flux having the physical properties set forth supra., we may compound between about 85 and 35 parts by weight of anhydrous magnesium chloride, 15 to 65 parts of sodium chloride, 2 to 20 parts of barium chloride, and 1 to 20 parts of calcium fluoride. However, a narrower range of variation is preferable, i. e. between about and 50 parts of magnesium chloride, 25 to 50 parts of sodium chloride, 5 to 10 parts of barium chloride, and 5 to 10 parts of calcium fluoride. Specifically, we may use about 60 parts by weight of anhydrous magnesium chloride, 40 parts of sodium chloride, 5 parts of barium chloride, and 10 parts of calcium fluoride, in preparing a suitable fiux.

'Another suitable magnesium chloride base fiux consists of between about 85 and 25 parts by weight of anhydrous magnesium chloride, 15 to 75 parts of potassium chloride, 2 to 20 parts of barium chloride, and 1 to 20 parts of calcium fiuoride. The narrower range of the foregoing compounds is between about 75 and 50 parts of magnesium chloride, 25 to 50 parts of potassium chloride, 5 to 15 parts of barium chloride, and 5 to 15 parts of calcium fiuoride. An example of a specific fiux employing the foregoing ingreclients, contains 65 parts of anhydrous magnesium chloride, 35 parts of potassium chloride, 10 parts of barium chloride, and 10 parts of calcium fiuoride.

The quantity and ingredients specified in the foregoing examples are not to be taken as a limitation on the invention, inasmuch as more or less variation in the proportions and character of Components is permissible without exceeding the scope of the invention.

The protective atmosphere which is employed l to prevent oxidation of the surface of the molten magnesium may be provided in various ways. For instance, a blanket of sulphur vapor may be maintained over the surface of the molten metal as by dusting sulphur powder upon the hot surface thereby excluding air from contact with the metal. Another way of protecting the metal is to displace the air normally in contact therewith with an atmosphere consisting of nitrogen, and/or carbon monoxide, carbon dioxide, sulphur dioxide, having incorporated therein a relatively small amount of carbon bisulphide. Still another protective atmosphere may be provided by maintaining an oxidation-inhibitng gas containing fluorine, either in its elemental or combined form, over the exposed surface of the molten metal, e. g. air containing the vapors of ammonium borofluoride, dichloro-diuoro-methane, etc.

The generation of a protective atmosphere of nitrogen and/or carbon monoxide, carbon dioxide, sulphur dioxide having incorporated therein a relatively small amount of carbon bisulphide may be accomplished in a ready manner. For instance, burning a substance such as sulphur, coke, natural gas, or the like, in air so as to cause the free oxygen therein to become combined, produces a suitable atmosphere. Carbon bisulphide is then vaporized into the products of the foregoing combustion to form a gaseous mixture which can be employed as the protective gas. The relative amount of carbon bisulphide in the protective gas mixture is capable of considerable variation, preferably the gaseous mixture should contain from about 1 to 10 per cent by volume of carbon bisulphide when nitrogen is employed, while somewhat larger amounts may be used with the other gases, viz., carbon monoxide, carbon dioxide, sulphur dioxide or mixture thereof.

The production of a fluorine-containing protective atmosphere may be accomplished in various ways. For instance, in a melting operation carried out in a closed melting crucible, if the fluorine compound selected is a solid at room temperatures and vaporizes below 850 F., a protective atmosphere can be produced over the surface of the molten metal by dropping. dusting, or otherwise placing the solid substance upon e the surface thereof, or upon a hot surface im- AIO mediately out of contact with the metal, or hy subliming the substances. with or without a diluent gas such as air, nitrogen, etc., and introducing the so-produced gas into the space over the surface of the metal to he protected. In the event that the fluorine compound selected is gaseous at ordinary room temperatures it can he stored in containers under pressure and passed with or without a diluent gas over the surface of the metal to he protected.

ong the suitable solid fluorine-containing compounds, are ammonium borofiuoride, am" monium silicofiuoride, anmonium fiuoride and ammonium fluophcsphate. Among the gaseous fiuorine-containing compounds which can he employed are boren trifluoride, silicon tetrafiuoride, and dichloro-difluoro-Inethana Referring now to the drawing, the melting crucible l is Suspended hy its rim 2 in the tilting iurnace 3 supported upon the trunnions d carried by the standard 5. The furnace 3 is adapted to he tilted hy movement of the lever 6 to rotate the furnace upon the trunnions 4. The furnace is heated with. a gas or oil burner 7. The crucible is provided with a substantially tight cover d bolted thereto. The cover 8 has an opening 9, provided with a hinged cover li), for charging metal and flux therethrough and to provide access to the crucibie contents for puddling. The crucible is provided with a removable pourng spout ll. The spout :ii is closed with a hinged cover 12 to which is attached a handle 13. A vertical feeder pipe i i, closable by a valve 15, surmounts the crucihle cover 8, connecting the automatic ieeder mechanism 16 with the crucihie i. A pipe J? controlled hy 'valve 18 connects with the pip The flux 20 is interposed hetween the cruoible i. and the metal 19.

The melting and purifying of magnesium and the pouring oi' castings from molten metal in the tiiting crucible iliustrated in the drawing will now he described briey with reference to the fiux and protective atmosphere described supra. in starting the operation with a cold crucible, a charge of inagnesium is placed therein, and a suitable r'lux is added in amount dependent upon the purity of the raw metal, the more impure the metal the more ux being required. In general, it is desirahie to maintain in the crucihle between about 2 and about per cent of fiux based on the weight oi' magnesium, although slightly more, e. g. up to about per cent, may he used in starting operation. An atmosphere substantially non-reactive with the magnesium is maintained over the surface of the metal. if a gaseous medium is to be supplied to the crucible to protect the metal therein, the valve 15 in the vertical feeder pipe is closed and the gas admitted through the pipe 17. On the other hand, if a' solid substance such as sulphur, ammonium horo fiuoride, etc., is to be utilized in generating the protective atmosphere then the valve 18 is closed, valve 15 opened, and the substance dropped through the pipe 14 from the feeder mechanism id upon the metal. The crucible is heated to melt the magnesium therein and the molten magnesium is puddled to cause the impurities to he absorbed by the iiux. The fiux is allowed to settle and the purified metal can then be poured into a mold or ladle by tilting the crucible to cause the metal to run out of the pouring spout.

Intermittent pourings can be made by tilting the crucible, until the charge of metal in the crucible is substantially reduced, at which time more metal is introduced thereinto. Flux may be added rrom time to time as required, care heing exercised that suiiicient flux is present to permit maintaining an appreciable amount in a fluid condition. If the iiux is permitted to hecome pasty hy absorption of impurities i'rom the metal, it will interfere with the film on the crucible walls and metal may then adhere thereto with consequent oxidatlon. A simple test to determine whether or not more flux is needed is readily made by observing whether flux is brought to the surface in the puddling operation. If none appears, fiux should he added, usually with the next charge of metal. As the crucible is operated over a period of time a siudge consisting of flux containing impurities from the metal will accumulate in the bottom of the crucible. This sludge is periodicaly removed, preferably when the charge of metal in the crucible is low. To remove the sludge the pouring spout il is taken off, the crucible is tilted as far as ,possible without spilling metal, and a sludge tool is inserted through the opening in the cover made by removal of the spout. This tool is a periorated iron plate or" suitable dimensions, say tour inches in diameter, attached at its center to the end of an iron rod. The tool is dragged rake- .tashion through the flux body in the crucible and pasty sludge scraped up and over the crucible edge. i'he fluid iiux and molten metal run around the edge and through the perforations in the tool and are not removed from the crucible.

The following example is iliustrative of 'the results ohtained in carrying out our invention. The apparatus used was suhstantially the same as that shown in the drawing and described supra. hmnonium horofiuoride was red upon the surface of the metal to produce the protective atinosphere thereover. A charge consisting of 100 pounds oi ingot metal, 53 pounds of scrap and :L

pounds oi ilux was placed in the melting crucible, The scrap was a foundry scrap of relatively clean quality. The iiux was compounded' hy melting together 75 parts of calciurn chloride, parte of sodium chloride, 5 parte of harium chloride and 5 parts of calcium fluoride. li'he ingot metal and scrap was a commercial magnesium alloy consisting of 93.7 per cent magnesium, 6 per cent aluminurn and 0.3 per cent manganese.

The change was melted down and puddled. There was then poured from the crucible ll' :sounds of castings, after which a charge of 80 pounds of ingot metal and 67 pounds of scrap was added to the crucible, This was melted down, puddled, and 127 pounds of castings was poured. At this time 7 pounds of sludge was removed. co pounds oi ingot and pounds of scrap was then introduced into the crucible, and the crucible was allowed to cool down overnight.

In the morning the crucihle was heated to melt the contents, puddled, and 120 pounds of castings poured. The next charge consisted or" 61 pounds of ingot metal, 60 pounds of scrap and 4.5 pounds of fiux or a composition as last described supra. This was melted, puddled, and 117 pounds of castings was poured and thento pounds of ingot metal and 60 pounds of scrap was added to the crucible, melted and puddled. '119 pounds of castings was poured and 59 pounds of ingot and 69 pounds of scrap was introduced into the orucible.

lil&

After melting and puddling this, 171 pounds of castings was poured and the crucible was then cleaned out, 28 pounds of sludge being removed.

In all, 789 pounds of metal was introduced into the crucible, and '171 pounds poured and cast, showing a loss of 18 pounds or only 2.1 per cent based on the weight of metal melted. The amount of flux used was 24.5 pounds, or 3 per cent based on the weight of metal melted. The amount of ammonium borofiuoride fed into the crucible to produce the protective atmosphere over the surface of the metal was approximately 2 pounds, or 0.25 per cent based on the weight of metal meited. The temperature of the metal was in all cases between 1350 and 1450" F. before pouring. The total series of pours was six, there being however, between 15 and 20 individual castings made during each series. This run lasted over a period of two days with cooling down overnight between the second and third series of pours.

At the beginning and at the end of each series of pours two molds of tension test coupons of 4 bars each were cast. The average ultimate strength of the 12 sets of bars was 29,500 ppunds per square inch, which shows the exceptionally good results obtained in the practice of our invention. Moreover, the test bars cast at the beginning and end of the last pour had an' average ultimate strength of 31,300 and 30,700 respectively as compared with 28,500 and 29,800 respectively for the bars cast at the beginning and end of the first pour. This clearly shows that there is no decrease in the quality of castings intermittently poured from magnesium processed in our improved manner. The foregoing variations of strength are well within the normal variation for cast magnesium alloys. The run described lasted only two days, but we have operated a crucible continuously for over a month, pouring thousands of castings with equally good results. In' accordance with the practice of our' invention as hereinbefore set forth the difficulties inherent to heretofore known methods for processing magnesium are eliminated. The oxidation of the metal during processing in a tilting crucible is prevented; a method is provided to maintain a body of magnesium in molten condition ready for pouring castings at intermittent intervals; material loss of metal caused by oxidation during the tilting operation is avoided; the inclusion of flux in magnesium castings is eliminated; and, in general, the meltin purifying, alloying and pouring of magnesium in a more simple, economical, and eflicient way is expedited.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the process herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

We therefore particularly point out and distinctly claim as our invention- 1. In processing molten magnesium in a tilting crucible, the steps which comprise maintaining in the crucible a fluid flux which is heavier than the magnesium, does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; and supplying a protective atmosphere over the metal.

2. In processing molten magnesium in a tilting crucible, the steps which comprise maintaining in the crucible a fluid flux which is heavier than the magnesium, does not spread over the top surface thereof,-and' substantially prevents the magnesium from adhering to the crucible wall; and supplying a fluorine-containing atmosphere over the metal.

3. In processing molten magnesium in a tilting crucible, the steps which comprise maintaining in the crucible a fluid flux which is heavier than the magnesium, does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; and supplying an atmosphere of sulphur vapor over the metal.

4. In processing molten magnesium in a tilting crucible, the steps which comprise maintaining in the crucible a fluid flux which is heavier than the magnesium, does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; and supplying an atmosphere comprising nitrogen containing carbon bisulphide over the metal.

5. In processing magnesium, the steps which consist in placing a body of magnesium in a covered tilting crucible; adding thereto a flux which in the fluid condition, is heavier than the magnesium does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; heating the crucible while maintaining over the magnesium a protective atmosphere; and pouring molten magnesium from the crucible.

6. In melting magnesium, the steps which consist in placing a body of magnesium in a covered tilting crucible; adding thereto a' fiux which, in the fluid condition, is heavier than the magnesium, does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; heating the crucible to melt the magnesium therein while maintaining thereover a protective atmosphere; and pouring molten magnesium from the crucible.

7. In processing magnesium, the steps which consist in placing a body of magnesium in a covered tilting crucible; adding thereto a fiux which, in the fluid condition, is heavier than the magnesium, does not spread over the top surface thereof, and substantially prevents the magnesium from adhering to the crucible wall; heating the crucible to maintain the magnesium in molten condition; maintaining a protective atmosphere over the magnesium; puddling the crucible contents to purify the molten magnesium; and pour-- ing molten metal from the crucible.

8. In melting magnesium, the steps which consist in placing magnesium in a covered 'tilting crucible; introducing into the crucible a flux consisting of between about 80 and about 30 parts by weight of calcium chloride, between about 20 and about 70 parts of sodium chloride, between about 1 and about 20 parts of calcium fiuoride, and between about 2 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere comprising a gaseous mixture of carbon bisulphide vapor and a gas selected from the group consisting of nitrogen, carbon monoxide,140 carbon d oxide and sulphur dioxide; and pouring molten magnesium from the crucible.

9. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of between about 75 and about 60 parts by weight of calcium chloride, between about 25 and about 40 parts of sodium chloride, between about 5 and about 10 parts of calcium fiuoride, and between about 5 and about 10 parts of barium ,94o,619 chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere comprising a gaseous mixture of carbon bisulphide vapor and nitrogen; and pouring molten magnesium from the crucible.

10. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of about 65 parts by weight of calcium chloride, about 25 parts of sodium chloride, about 5 parts of calcium fluor-ide, and about 5 parts of barium chloride; heating the crucible to melt the magnesium therein while maintainig thereover an atmosphere comprising a gaseous mixture of carbon bisulphide vapor and nitrogei; and pouring molten magnesium from the crucible.

11. In melting magnesium, the steps which consist in placng magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of between about and about 30 parts by weight of calcium chloride, between about 20 and about 70 parts of sodium chloride, between about 1 and about 20 parts of calcium fluoride, and between about 2 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover a fluorine-containing atmosphere; and pouring molten magnesium from the crucible.

12. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of between about 75 and about 60 parts by weight of calcium chloride, between about 25 and about 40 parts of sodium chloride, between about 5 and about 10 parts of calcium fluoride, and between about 5 and about 10 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover .an atmosphere containing a relatively small amount of a compound selected from the group consisting of ammonium borofluoride, ammonium silicofiuoride and ammonium fiuophosphate; and pouring molten magnesium from the crucible.

'13. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of about 65 parts by weight of calcium chloride, about 25 parts-of sodium chloride, about 5 parts of calcium fluoride, and about 5 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere containing a relatively small amount of ammonium borofluoride; and pouring molten magnesium from the crucible.

14. In melting magnesium, the steps which consist in placing magnesium in a covered tiltiug crucible; introducing into the crucible a flux consisting of between about and about 35 parts by weight of magnesium chloride, between about 15 and about 65 parts of sodium chloride, between about 1 and about 20 parts of calcium fluor-ide, and. between about 2 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere comprising a gaseous mixture of carbon bisulphide vapor and a gas selected from the group consisting of nitrogen, carbon monoxide, carbon dioxide, and sulphur dioxide; and pouring molten magnesium from the crucible.

15. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux consisting of between about 75 and about 50 parts by weight of magnesium chloride, between about 30 and about 50 parts of sodium chloride, between about 5 and about 10 parts of calcium fluoride, and between about 5 and 10 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere comprising a gaseous mixture of carbon bisulphide vapor and nitrogen and pouring molten magnesium from the crucible.

16. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing into the crucible a flux con-' sisting of about 60 parts by weight of magnesium chloride, about 40 parts of sodium chloride, about .about 1 and about 20 parts of calcium fluoride,

and between about 2 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover a fluorine-containing atmosphere; and pouring molten magnesium from the crucible.

18. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible; introducing 'into the crucible a flux consisting oi' between about 85 and about 25 parts by' weight of magnesium chloride, between about 15 and about 75 parts of potassium chloride, between about 2 and about 20 parts of calcium fluoride, and between about 1 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover an atmosphere comprising a gaseous mixture of carbon bisulphide `vapor and a gas selected from the group consisting of nitrogen, carbon' monoxide, carbon dioxide, and sulphur dioxide; and pouring molten magnesium from the crucible.

19. In melting magnesium, the steps which consist in placing magnesium in a covered tilting crucible: introducing into the crucible a flux consisting of between about 85 and about 25 parts by weight of magnesium chloride, between about 15 and about 75 parts of potassium chloride, between about 2 and about 20 parts of calcium fluoride, and between about 1 and about 20 parts of barium chloride; heating the crucible to melt the magnesium therein while maintaining thereover a fiuorine-containing atmosphere; and pouring molten magnesium from the crucible. .i

EDWIN 0. BARSTOW. JOHN A. GANN. JOHN E. HOY. 

